This pipe is often made by the coppersmith from sheet copper, but it is better and cheaper to use lengths of seamless drawn pipe from the tube mill. The mill supplies pipe up to 8 inches, or possibly 10 inches in diameter. Larger pipes must be made from sheet copper.

A great advantage in the use of pipes made of copper is the safety and ease with which such pipes may be bent to suit the many crooks and turns necessitated by cramped machinery spaces. Thin-walled pipes (about No. 12 gage or thinner) are filled with melted rosin and heavier pipes are filled with dried sand to keep them from flattening when bent. A wood plug is driven in one end of the pipe, the entire length is filled with rosin or sand, and another plug is driven tightly in the other end. Rosin-filled pipes are bent cold and sand-filled pipes are bent hot. Bending is done in the hydraulic bending press, or by holding one end between two pegs or clamps and pulling the other end with a block and tackle. A length of pipe may be slipped over each end of the pipe to be bent to assist in holding and in increasing the leverage of the pulling force.

Bending causes kinks or wrinkles to form at the inner curvature Dr throat of the pipe. These must be carefully hammered smooth while the pipe remains filled. The copper along the outer surface of curvature, or back, of the bend is necessarily thinned somewhat in bending, hence the practice of selecting a pipe with walls two or more gages thicker than is otherwise required.

Large pipes, or those of any size bent to a curve of small radius, are, in high-grade work, bent in two stages, i. e., the pipe is filled and bent part way to the required radius, is emptied, annealed, refilled and bent to the full extent required.

Fig. 255.

Fig. 256. Copper Pipe Joints.

Small pipes may be bent, when filled, by means of the grooved formers shown in Fig. 251.